basically flake is usually a name given to an oversize pigment that isn't used in production but sometimes can be broadly used to also describe pearls and metallics or any size ,, ..
Pearl is a mica substrate coated with different layered thicknesses (usually TiO2 or FeO3) the thicker the optical thickness of the film will result in different colours being reflected and transmitted (geometric thickness x by its refrative index )
if the layers are very thin it will reflect a white pearl increasing the layer thickness will result in the colours in order of gold, red, blue and green ..
Refraction is basically when light enters a different medium eg .. water that has a higher density than air so the light will bend in the direction which will provide it with the quickest way out . The more the light bends to pass throught the denser medium the higher the refractive index will be ..
A good example is when light passes through water droplets in the air and creates a rainbow ..
the transmitted colour of a pearl is the weaker colour and is complemantary (opposite) to the reflected colour and will be noticed more over a lighter coloured base ,, rather than darker which will make the reflected angle look more intense ..
then theirs metallic which is an aliminum pigment that reflects all light like a mirror ..
hope this helps ..
